DP 2D models problems with two-dimensional state, typically comparing or aligning sequences. The pattern clicks when you identify how dp[i][j] relates to dp[i-1][j], dp[i][j-1], and dp[i-1][j-1].
You'll reach for 2D DP when comparing two sequences or counting paths in grids. If you can explain these concepts in your own words, you'll solve related problems faster under interview pressure.